J Magn Reson Imaging. 2022 Oct 31. doi: 10.1002/jmri.28509. Online ahead of print.
ABSTRACT
BACKGROUND: The measurement of the concentration of theranostic agents in vivo is essential for the assessment of their therapeutic efficacy and their safety regarding healthy tissue. To this end, there is a need for quantitative T1 measurements that can be obtained as part of a standard clinical imaging protocol applied to tumor patients.
PURPOSE: To generate T1 maps from MR images obtained with the magnetization-prepared rapid gradient echo (MPRAGE) sequence. To evaluate the feasibility of the proposed approach on phantoms, animal and patients with brain metastases.
STUDY TYPE: Pilot.
PHANTOM/ANIMAL MODEL/POPULATION: Solutions containing contrast agents (chelated Gd3+ and iron nanoparticles), male rat of Wistar strain, three patients with brain metastases.
FIELD STRENGTH/SEQUENCE: A 3-T and 7-T, saturation recovery (SR), and MPRAGE sequences.
ASSESSMENT: The MPRAGE T1 measurement was compared to the reference SR method on phantoms and rat brain at 7-T. The robustness of the in vivo method was evaluated by studying the impact of misestimates of tissue proton density. Concentrations of Gd-based theranostic agents were measured at 3-T in gray matter and metastases in patients recruited in NanoRad clinical trial.
STATISTICAL TESTS: A linear model was used to characterize the relation between T1 measurements from the MPRAGE and the SR acquisitions obtained in vitro at 7-T.
RESULTS: The slope of the linear model was 0.966 (R2 = 0.9934). MPRAGE-based T1 values measured in the rat brain were 1723 msec in the thalamus. MPRAGE-based T1 values measured in patients in white matter and gray matter amounted to 747 msec and 1690 msec. Mean concentration values of Gd3+ in metastases were 61.47 μmol.
DATA CONCLUSION: The T1 values obtained in vitro and in vivo support the validity of the proposed approach. The concentrations of Gd-based theranostic agents may be assessed in patients with metastases within a standard clinical imaging protocol using the MPRAGE sequence.
EVIDENCE LEVEL: 2.
TECHNICAL EFFICACY: Stage 1.
PMID:36315197 | DOI:10.1002/jmri.28509
